A fuel cell produces electricity by electrochemically consuming a fuel, typically hydrogen, and an oxidant, such as oxygen. Fuel cells are well known devices. Refer to FIG. 1, a prior art exploded view of a fuel cell. Generally, the fuel cell A has an anode electrode 10 for receiving the hydrogen and a cathode electrode 20 for receiving the oxygen. The anode electrode 10 is spaced from the cathode electrode 20 with an electrolyte 30 disposed therebetween. Each electrode includes a substrate with a catalyst layer (not shown) on one surface where the catalyst layer is in contact with the electrolyte. An anode and a cathode electrolyte reservoir plate 40 and 50 are disposed on either side of the anode and the cathode electrodes, respectively. The anode electrolyte reservoir plate 40 has grooves, represented by the groove 40a, for providing hydrogen to the anode electrode 10. The cathode electrolyte reservoir plate 50 has grooves, represented by the groove 50a, for providing oxygen to the cathode electrode 20. A separator plate 60 is disposed adjacent to the anode electrolyte reservoir plate 40. A separator plate 70 is disposed adjacent to the cathode electrolyte reservoir plate 50. Separator plates are well known components of fuel cell stacks. The separator plates act as a barriers to prevent the electrolyte from migrating from one fuel cell to another and to help prevent the mixing of the hydrogen and the oxygen disposed on opposite sides of the separator plate.
Refer to FIG. 2, a prior art exploded view of a fuel cell stack. The fuel cell stack S is composed of individual fuel cells A and A' aligned electrically in series.
In operation, referring to FIG. 2, the hydrogen from the electrolyte reservoir plate 40 contacts the anode catalyst layer (not shown) where it is converted into hydrogen ions and free electrons. The hydrogen ions migrate from the anode electrode 10 across the electrolyte 30 to the cathode electrode 20. Free electrons pass from the anode electrode 10' through the anode electrolyte reservoir plate 40' and separator plate 70 to the adjacent cathode electrolyte reservoir plate 50, and subsequently, the cathode electrode 20. At the catalyst layer of the cathode 20, the free electrons from the anode 10' and the oxygen react with the hydrogen ions from the anode 10 enabling this described electrochemical process to be continuous and to produce electrical power by the effective electron flow through the cell stack and its connected external circuit.
Due to the barrier function of the separator plates, they must be highly impermeable to the electrolyte and the hydrogen and oxygen. As mentioned above, the free electrons from one fuel cell are utilized by the adjacent fuel cell at the cathode catalyst. Since these electrons must travel through the separator plates, the separator plates must also be highly electrically conductive.
There are two major problems with conventional separator plates, which are: first, the separator plates' permeability increases over the operative life of the fuel cell stack; and, second, the separator plates are too expensive. Conventional separator plates initially maintain low permeability, but generally develop permeability which can decrease the efficiency of the fuel cell stack. When separator plates are manufactured, those that cannot be used decrease the yield and increase the cost per separator plate. Consequently, what is needed in the art is a high yield separator plate capable of substantially preventing permeability of reactants for at least about 40,000 hours of fuel cell stack operation.